Oil well drilling requires the pumping of specially compounded drilling muds at high flow rates in order to bail cuttings from the hole and control formation pressures. Penetration of a formation at times may result in pressure surges known as kicks, which can damage the pump or related equipment, and are undesirable in any case. Ball type check valves can be included in the drilling pipe string for the purpose of controlling down-hole back pressure, and such devices are effective in that regard. The necessity of fitting such a valve within the confines of the drilling pipe diameter compromises its fluid flow capacity so that increased mud pump pressure is required to overcome the restriction. This penalty tends to discourage the use of such valves.
Wells are also pressure treated with various special purpose fluids and mixtures on occasion, for remedial purposes such as stimulating production or extending the life of the well. The pressurized treatment medium may be a mud compound, cement, resin coated sand, gravel or some other material, depending upon the nature of the operation. Back pressure control requirements and the equipment used are much the same as for drilling practice, with similar compromises and limitations.
Flapper type valves such as the OTIS ENGINEERING CORPORATION "Series 10" and "Type Q" safety valves, are known to be used in production pipe strings where they are remotely controlled from the surface by hydraulic pressure. Other applications have been made of flapper type valves, used facing upwardly in the production pipe string, so as to allow free upward flow only. Prior to the instant invention however, no down hole pressure actuated flapper-type safety valve has been known to the industry.
The ball type check valves known to the art are capable of rapid closure during a pressure kick. It is an object of the present invention to retain this rapid response while providing an improved flow path compared to that of a ball type valve and thus a relatively low pressure drop. This reduced pressure resistance allows pumping of stiffer, more viscous mixtures by reducing the necessary pumping pressure and can also improve pump life. It is also an object to provide the valve of the present invention in a form adaptable to the various tubing and pipe diameters and to the different joint thread standards used in the industry.